Abstract

A rigorous theoretical analysis of a fiber optic surface plasmon resonance sensor is presented. The sensor is based on the spectroscopy of mixed surface plasmon – fiber cladding modes excited by the fundamental mode of an optical fiber via a Bragg grating formed in the fiber core. The transmission spectrum is calculated by means of the Coupled Mode Theory. The modal structure is theoretically analyzed using a 3-D method based on a field expansion approach for matching the field continuity at the boundary of the layers. The theoretical analysis revealed a series of narrow transmission dips associated with the coupling of the fundamental mode to the mixed surface plasmon – fiber cladding modes. The sensitivity of these dips to changes in the refractive index of the analyte is calculated. Moreover, the refractive index resolution of the sensor was estimated to be better than 2 × 10−6 RIU.

FWHM wμ of the transmission dip corresponding to 134th - 140th cladding mode as a function of rg. (solid line, left axes). The transmittance at a resonance Tμrescorresponding to the mode 134th - 140th cladding mode as a function of rg. . (dashed line, right axes). nsur = 1.325.